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United States Patent |
6,157,320
|
Yujiri
,   et al.
|
December 5, 2000
|
Enhanced paint for microwave/millimeter wave radiometric detection
applications and method of road marker detection
Abstract
Adding a quantity of metallic shot or particles of other materials having a
high dielectric constant to the thermoplastic paint in the mixing pot of
ordinary roadway marker fixation equipment, which extrudes the paint and
applies same to the roadway surface, enhances the MMW radiometric
visibility of the marker without adverse effect to the affixation
equipment. Vehicles containing MMW radiometers directed down toward the
roadway surface moves along the roadway surface is able to automatically
sense microwave/millimeter wave energy from a marker in the vehicles path.
In one system, the sensed energy is used in conjunction with other
apparatus to assist to guide the vehicle within a traffic lane. In another
system, the sensed energy is decoded and displayed as pertinent
information for the vehicle's driver.
Inventors:
|
Yujiri; M. Larry (Torrance, CA);
Hauss; Bruce I. (Los Angeles, CA);
Quon; Bill H. (Aliso Viejo, CA);
Eninger; James E. (Torrance, CA)
|
Assignee:
|
TRW Inc. (Redondo Beach, CA)
|
Appl. No.:
|
342786 |
Filed:
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June 29, 1999 |
Current U.S. Class: |
340/901; 180/167; 180/168; 180/169; 340/905; 340/933 |
Intern'l Class: |
G08G 001/00 |
Field of Search: |
340/901,933,941,904,905
180/167,168,169
|
References Cited
U.S. Patent Documents
3725930 | Apr., 1973 | Caruso | 343/100.
|
3998645 | Jul., 1975 | Okazki | 106/30.
|
4518722 | May., 1985 | Shutt | 523/135.
|
4600642 | Jul., 1986 | Lodge et al. | 428/367.
|
4621265 | Nov., 1986 | Buse | 342/169.
|
4758469 | Jul., 1988 | Lange | 428/325.
|
4916014 | Apr., 1990 | Weber | 428/403.
|
5039557 | Aug., 1991 | White | 427/137.
|
5202742 | Apr., 1993 | Frank | 365/5.
|
5493291 | Feb., 1996 | Bruggemann | 340/905.
|
5516227 | May., 1996 | Kozak | 404/9.
|
5530330 | Jun., 1996 | Baiden et al. | 318/580.
|
5875408 | Feb., 1999 | Bendett et al. | 70/23.
|
Foreign Patent Documents |
0135740 | Apr., 1985 | EP | .
|
2237862 | May., 1991 | GB | .
|
9621700 | Jul., 1996 | WO | .
|
Other References
Yujiri et al, Passive Millimeter-Wave Imaging, Quest Magazine, TRW, Inc.
1990-1991, vol. 13, No. 2.
|
Primary Examiner: Hofsass; Jeffrey A.
Assistant Examiner: Nguyen; Tai T.
Attorney, Agent or Firm: Yatsko; Michael S., Goldman; Ronald M.
Parent Case Text
This application is a divisional of copending application Ser. No.
08/864,249 filed on May 28, 1997.
Claims
What is claimed is:
1. A system for communicating to a vehicle operator operating a vehicle
upon a roadway in a geographic region in which the roadway is exposed to
the sky of the presence nearby of a roadway marker strip on said roadway,
comprising:
MMW radiometer means carried by said vehicle for detecting MMW radiometric
energy;
said MMW radiometer means including antenna means oriented forwardly and
downwardly at a steep angle toward said roadway;
a roadway marker comprising MMW radiometric energy reflecting material,
said roadway marker forming a strip adhered to said roadway and
essentially flush therewith;
said roadway marker having a MMW radiometric temperature characteristic
distinct from and provides detectable MMW radiometric contrast with the
MMW radiometric temperature characteristic of said roadway.
2. A roadway marker system comprising a roadway marker on a roadway
surface; and a MMW radiometric detector carried by a vehicle for providing
MMW radiometric detection of said roadway marker, said MMW radiometric
detector including means for sensing MMW radiometric energy emissions and
reflections from a small area of roadway surface below said vehicle, said
roadway having a first MMW radiometric temperature characteristic and said
roadway marker having a second MMW radiometric temperature characteristic
distinct from said first MMW radiometric temperature characteristic.
Description
FIELD OF THE INVENTION
This invention relates to new roadway marking systems, and, more
particularly, to an enhancement to roadway marker paints that renders the
road markers more distinguishable from the adjacent and/or underlying
pavement when viewed at microwave/millimeter wave radiometric frequencies.
The invention also relates to a method for ascertaining the presence of
roadway markers and information coded in such markers by application of
passive radiometric energy sensitive inspection apparatus within an
electronic control and/or warning system.
BACKGROUND
Roadway marking systems have long been used to provide vehicular equipment
operators with pertinent information through the medium of roadway
markers. As example, the white stripe painted on the roadway in front of a
stop sign, familiar to the lay reader, provides a vehicle operator, the
driver, with a physical limit or boundary that the driver's approaching
vehicle should not exceed in coming to a full and complete stop in
obedience to the stop sign. On multi-lane roadways, the lanes are
delineated by roadway markers. And, at major airports service roads and
corridors are often distinguished, in addition to signal lamps, by painted
lines marking the borders to the service road, providing a visible guide
for the pilot. The foregoing are but a few of the most common
applications.
In more recent experience, roadway markers have also been adapted as part
of vehicular guidance and control systems. The information provided by the
roadway markers is used to automatically issue an alarm or steer and/or
position a moving vehicle. Sensors on the vehicle detect a marked path
along a roadway and the associated control equipment on the vehicle is
able to automatically correct the vehicle's steering should the sensor
detect the vehicle's departure from the marked path. From time to time
newspapers report of experimental automobile control systems that are
intended to automatically control and guide a vehicle's travel along a
highway, eliminating the need for the driver's complete attention.
Examples of the foregoing appear in the patent literature. The system in
U.S. Pat. No. 5,202,742 to Frank et al carries a laser radar carried on
the vehicle to detect reflective markers along a roadway. The laser beam
is scanned over the roadway and the associated detectors, which receive
light reflected from the roadway markers, are used by associated control
equipment on board the vehicle to guide the vehicle relative to the
roadway markers. Another system is presented in U.S. Pat. No. 4,947,094 to
Dyer et al. In the Dyer system a linear charge coupled device (CCD)
carried by an industrial warehouse vehicle, such as a forklift, monitors
the position of a track, such as formed by a painted line on the warehouse
ceiling overlying the roadway. The CCD images that line and that imaging
allows the control equipment in the system to steer the industrial vehicle
along the track.
Though painted white stripes are often used, the better roadway markers are
formed of a thermoplastic material, supplied by the manufacturer as minute
plastic granules or beads, that is heated to place the material into the
liquid form, which can flow. Often small spheroidal glass particles are
mixed into the ingredients as part of the liquid. That hot liquid is
coated or extruded in a thin strip onto the roadway surface, where the
plastic material is allowed to cure, that is, solidify and harden. The
plastic material is designed to seep into the rough surface and pores
characteristic of pavement materials, such as cement and asphalt, and
hardens to form a firm grip or bond to the pavement.
Such marker is relatively wear resistant, enduring the heavy pounding and
friction of automobile tires. It resists the effects of snow and rain. It
also resists to the deleterious effects of sunlight, including that from
ultra-violet radiation. And it maintains its color for years, ensuring a
visible contrast with the surface of the roadway. Although those who apply
the marker to the roadway refer to the thermoplastic film simply as
"paint", an analogy to house paint, a reference that carries forward in
the subsequent description, roadway markers are understood as a serious
field of endeavor.
It is noted that the exact composition of the various thermoplastic
ingredient materials suitable for pavement marker application, not known
to the present applicants, is well known to those skilled in the road
marker art. As becomes apparent those details are not necessary to an
understanding of the present invention and, hence, need not be further
described. Those interested in learning more on that subject, may make
reference to the technical literature in that field.
The foregoing marker and control systems make use of reflected light, that
is, the visible region of the electromagnetic energy spectrum, and that
light originates either naturally in the environment or is generated by a
light source in the detection system. Other forms of energy, though not
perceptible directly by human senses, are known and have also been applied
in detection schemes. As one finds from the scientific literature, the
electromagnetic energy spectrum extends over a wide range of wavelengths,
extending at least from the shortest wavelengths, those in the
ultra-violet region and below, to and beyond the longest wavelengths in
the infra-red regions. One finds visible light in this spectrum, a region
which human eyes are able to detect and which enables our vision, and also
radio waves. The microwave spectrum lies in a portion of that radio
spectrum; and in an end portion of that microwave spectrum, one finds the
millimeter wave region.
Microwave and millimeter wave energy is emitted naturally from all objects.
It is also incident on our Earth from outer space, and from the Earth's
atmosphere, a gaseous object, irradiating, among other things, the
roadways on which we travel. Since outer space is very cold, approximately
four degrees Kelvin, and since the amount of energy emitted is
proportional to the emitting objects physical temperature, very little
energy is incident from outer space. For the most part the incident
microwave/millimeter wave energy incident on the roadway is from the
atmosphere itself, which serves or acts roughly speaking like a forty
degree Kelvin emitter at a 94 GHz frequency. This energy, in part, is
reflected from the materials on which it is incident, including the
roadway and markers on the roadway. Those materials also emit a like kind
of energy, and, since those materials are typically at "room temperature",
300 degrees Kelvin, they appear warmer, higher in temperature, than those
materials that principally reflect the "cold sky".
In fact, according to Planck's radiation law, any perfectly absorbing body
emits radiation at all frequencies of the energy spectrum. For most
natural objects in our environment, such radiation is relatively high in
the infra-red region of the energy spectrum, proportional to the fourth
power of the object's physical temperature. At microwave/millimeter wave
frequencies, the energy is much less, varying only directly with the
temperature. Though less intense, that microwave/millimeter wave energy is
detectable and measurable with properly designed microwave/millimeter wave
radiometers.
Microwave/millimeter wave radiometric detectors are microwave/millimeter
wave receivers that detect the total power received. A
microwave/millimeter wave radiometer is, in effect, a highly sensitive
total power receiver. The receiver receives its signals from a directional
antenna, such as a microwave/millimeter wave horn antenna, whose receiving
"footprint" or field of view is directed at the element or area to be
observed. The magnitude of the signal received by the radiometer is
proportional to the temperature of the object under observation, and/or
the temperature reflected by the object, depending upon the percentage and
types of objects within the antenna's footprint and the object's
emissivity .epsilon., the latter being equal to (1-.rho.), where .rho. is
the object's reflectivity. Radio astronomers have long used radiometric
detectors to scan the heavens to detect planetary bodies and stars.
For convenience, the term, microwave/millimeter wave, is hereafter
sometimes abbreviated to MMW. Thus, when used to modify the term
radiometer, the abbreviated term distinguishes the radiometer discussed in
connection with the present invention from other known types of
radiometers, such as infra-red radiometers.
Radio astronomers also earlier determined the existence of "propagation
windows" through the atmosphere for millimeter wave energy, frequencies in
the 30 to 300 GHz range, at which the attenuation is relatively modest in
both clear air and fog. That is, transmission of millimeter wave energy
from outer space at those "window" frequencies are not attenuated in
propagating through overlying clouds to their ground based radio
telescopes as greatly as adjacent higher or lower frequencies in the
millimeter wave region about that frequency. Similarly, the atmosphere
does not emit as much energy in these windows, and, therefor does not
"wash out" or overpower signals from space. These windows occur at 35 GHz,
94 GHz, 140 GHz and 220 GHz.
Imaging of ground objects, including aircraft runways, using MMW
radiometric energy and MMW radiometric detectors, was proposed in the
past. U.S. Pat. No. 3,725,930 to Caruso uses a microwave radiometer to
detect a pattern of radiometric energy reflecting markers on an airport
runway. Metal, such as iron, is known as a good MMW radiometric reflector;
it is of high .rho.. In Caruso's system, wedge shaped metal plates, of a
size between two feet and twenty feet in diameter, are placed on the
runway as markers to provide a surface tilted up from the runway surface
as presents a ramp to the oncoming airplane. Microwave energy from a
portion of the cold sky is thereby reflected toward radiometric detectors
carried on the taxiing aircraft, and, thus, such markers stand out from
the surrounding landscape as cold looking.
Although Caruso does not expressly describe the height of the metal ramps
thus employed, one appreciates that any protrusion from the roadway
surface poses an impediment to the taxiing airliner and other airport
vehicles using the runway. At a minimum such obstacles would cause the
aircraft to sustain a series of bumps, as might disturb the passengers,
and, if great enough in height, would present an obstacle that would
render Caruso's system impractical of application.
Placed on the runway, the large metal plate is visible to view and does not
have the anonymity of a painted stripe. It can easily be removed from the
roadway surface. The metal plate thus provides an attraction to those
pranksters or unscrupulous persons who would detach and sell the metal as
scrap, disabling a key element of the marker system. That visibility is an
unfortunate practical drawback.
Further, in an article published by the assignee of the present invention
"Passive Millimeter-Wave Imaging", Yujiri et al, Quest Magazine, TRW, Inc.
1990/1991, Vol. 13, No. 2, the authors, including one of the present
inventors, present two dimensional pictures of the radiometric image of an
airport, harbor and other scenes taken with experimental apparatus
containing radiometric detectors tuned to receive energy at a frequency of
94 GHz. Though the images are of low resolution, the viability of
radiometric inspection is demonstrated as technically feasible and urged
as a soon-to-be practical means to achieve images of scenes, despite rain
and fog weather conditions. The article predicts additional technical
development, and, though offering suggestions for radiometric imaging, the
article offers no guidance on improving roadway marker systems.
Accordingly, an object of the present invention is to provide a new method
for detecting roadway markers, one that uses MMW radiometers;
It is another object of the invention to provide a roadway marker detection
and control system that is passive and does not require transmitting
apparatus that emits electromagnetic energy;
It is a further object of the invention to provide a roadway marker paint
having enhanced contrast with the adjoining roadway surface at MMW
radiometric frequencies, a true "microwave/millimeter wave radiometric"
paint; and
It is a still further object of the invention to provide an enhanced
radiometric paint that may be applied to roadway surfaces using existing
unmodified paint striping equipment.
SUMMARY OF THE INVENTION
In accordance with the forgoing objects, an improved roadway marker
detection method employs a vehicle or other wheeled platform capable of
movement along the roadway surface. The vehicle supports a downwardly
inclined looking radiometer a short distance above the roadway. The
vehicle is then moved along the roadway and the MMW radiometric energy,
reflected and/or emitted from the various patches of road surface and
viewed as the vehicle progresses forward, is monitored and may be
displayed. Any roadway markers encountered along the way are detected by a
significant decrease in energy received by the radiometer as a result of
viewing energy from the "cold" sky.
Unlike prior systems, the foregoing method distinguishes markers in rain or
fog and in day or at night, with wet or snow covered roadways. Markers are
detected passively. It is not necessary to emit electromagnetic radiation
into the environment to make the detection, minimizing risks to personnel
and avoiding possible interference to other electronics equipment.
Moreover, since artificial illumination is unnecessary, the roadway
infrastructure requirements are simplified.
In accordance with another aspect to the invention, a new roadway marker
paint possesses enhanced MMW radiometric energy reflection characteristics
obtained by incorporation of metal particles and/or high dielectric
particles within the thermoplastic material of ordinary road marker paint.
A preferred embodiment of the enhanced radiometric paint includes size 20
or 30 iron shot with the iron shot comprising approximately 30% of the
paint mixture by volume.
When the foregoing inspection procedure is made of markers constructed in
that way, the decrease in detected temperature is larger than before on
some surfaces, such as asphalt, although the change is not as great on
concrete. This evidences an increased radiometric contrast between the
marker and the adjacent pavement. As a benefit the new radiometric paint
may be applied to the roadway using existing paint striping equipment.
With the increase in contrast between the radiometric energy reflecting
characteristic of the marker and that of the roadway, a more pronounced
measurement is available for detection. With increased signal, the signal
to noise ratio is improved and detection is possible even if the
sensitivity of the detector lowers with age.
The foregoing and additional objects and advantages of the invention
together with the structure characteristic thereof, which was only briefly
summarized in the foregoing passages, becomes more apparent to those
skilled in the art upon reading the detailed description of a preferred
embodiment, which follows in this specification, taken together with the
illustration thereof presented in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the Drawings:
FIG. 1 pictorially illustrates the apparatus for carrying out the new
method of detecting and interrogating roadway markers;
FIG. 2 is a block diagram of the electronic apparatus used in performing
the method of FIG. 1;
FIG. 3 is a chart illustrating radiometric measurements taken on a roadway
using the apparatus of FIG. 1 in the novel method;
FIG. 4 illustrates the relationship between a roadway marker and different
antenna fields of view;
FIG. 5 illustrates an embodiment of the enhanced MMW radiometric paint of
the invention in section view and applied to a roadway surface;
FIG. 6 is a bar chart showing the enhanced results obtained with the
improved paint and a comparison with the other materials taken under like
conditions;
FIG. 7 pictorially illustrates a truck fitted with MMW radiometric
detectors that use the novel roadway marker system to assist in
positioning the truck within a roadway traffic lane;
FIG. 8 is a block diagram of the electronic system for the truck of FIG. 7
for providing lane positioning information to the vehicle driver; and
FIG. 9 pictorially illustrates a vehicle equipped with a passive MMW
radiometric lane tracking system as in FIG. 7 and also equipped with a bar
code information system using the same electronic system as in FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference is made to FIG. 1 which pictorially illustrates the new method
for observing roadway markers. As illustrated in FIG. 1 a MMW radiometer
assembly or radiometer, represented by block 1, is mounted at the front
end of a wheeled cart 3 and at a predetermined height above the roadway 5.
A marker 7 of predetermined width forms a stripe that extends at least
partially across the roadway, in a direction perpendicular to the sheet of
paper.
The MMW radiometer, which is of any known construction available in the
marketplace, is suitably tuned to 94 GHz, is of a bandwidth of
approximately 1 GHz or less and has attached a small aperture receiving
antenna or horn 2 that is oriented downward at a steep angle to the road
surface, suitably an angle, .alpha., from the vertical of about 20
degrees. The vertical position of the radiometer is adjustable by means of
a track mounting 9 or equivalent, and, preferably, is positioned with the
front end of feed horn 2 positioned approximately eight inches above the
roadway.
It will be found that the MMW radiometric energy sensed at the MMW
radiometer as reflected from a given material is subject to many variables
including, but not limited to, the distance from the reflecting surface,
the angle at which the antenna input is oriented relative to the surface,
the polarization, horizontal or vertical, of the energy being sensed, and
the frequency of that energy within the electromagnetic spectrum. The
foregoing represents the present preference for those variables.
FIG. 2 is a block diagram of the system electronics, showing the MMW
radiometer 1 and its associated antenna 2 and the display 11, which may be
a meter or a cathode ray tube monitor. The MMW radiometer outputs a
voltage to the display. Other forms of output can be used independently or
collectively as desired. A chart recorder 18 may be connected to receive
the output and provide a continuous plot of values as the cart is moved
along a predetermined path. A visual monitor circuit 20, can be calibrated
to provide an output, such as lighting a lamp, that gives a visually
perceptible indication when the temperature falls to a predetermined
level, as when the MMW radiometer detects a marker.
MMW radiometer 2 is of any known type. It is an electrically powered radio
receiving device and may be supplied with necessary electrical current to
energize the MMW radiometer by a battery, not illustrated, carried on the
cart or other conventional power supply. As example, a MMW radiometer
marketed by the Millitech company of South Deerfield, Mass. is suitable
for the procedure. Miniaturized MMW radiometers based on the
microwave/millimeter wave monolithic integrated circuit technology, "MMIC"
are available for 40 GHz operation through a distributor from the TRW
company, assignee of the present application, and are expected to be
available for 94 GHz operation in the near future. Miniaturized
radiometers are preferred, particularly for the specific embodiments of
the invention herein described. An output from the MMW radiometer is
connected to an associated cathode ray tube display or digital or analog
signal monitor 11 to permit the operator to view the radiometric
temperature being sensed at the antenna 2.
In operation, with the MMW radiometer energized and operating, the cart is
pushed or, if a self-propelled motorized structure moves forward, to the
right in the figure, rolling forward on its wheels 4. As represented in
the figure in dotted lines, 2b and 2a as the cart progresses forward the
antenna moves horizontally. Looking down the antenna senses MMW
radiometric energy, .lambda., emitted and reflected from the roadway
surface.
As described in the background to this specification, microwave/millimeter
wave energy referred to as MMW radiometric energy originating from the
other planets, stars and atmosphere is incident on the earth, including
roadway 5 and marker 7. This MMW radiometric energy arrives from all
directions in the sky overhead, over essentially a hemisphere of overlying
sky. The only exception is that portion of the sky that may be blocked or
attenuated by the cart and the apparatus carried on that cart. The
incident MMW radiometric energy penetrates the marker and the surface of
the roadway. Since all materials reflect MMW radiometric energy, some
materials to a greater extent than other materials, some of that MMW
radiometric energy is reflected or "back scattered" into the receiver horn
2.
The product of emissivity of an object, .epsilon., and true physical
temperature of the object equals its brightness temperature or, as
otherwise termed, its radiometric temperature. A perfect absorber has an
emissivity of 1.0 and is known as a black body and a perfect reflector has
an emissivity of zero. The emissivity of an object, which is polarization
dependent, is, for each polarization, vertical or horizontal, a function
of the dielectric constant, the body's surface roughness, and the angle of
observation. As measured at an angle of 90 degrees to the surface, that
is, looking straight down, the emissivity of an object at frequency of 94
GHz such as bare metal is 0.040, dry gravel is 0.921, dry asphalt is
0.914, dry concrete is 0.905, dirt is 1.0.
The apparent temperature being radiated by an object is a combination of
three sources and may be respresented by the following equation:
T=.epsilon.a+.rho.Ts+.tau.Tb,
where, .rho. and .tau. are the emissivity, reflection and transmissivity
coefficients, respectiviely; and Ta, Ts and Tb are the ambient
termperature of the material, the reflected sky temperature and the
temperature of the background behind the object, respectively. For
metallic materials .tau.Tb is negligible and may be ignored.
Antenna 2 receives MMW radiometric energy that is reflected in the
foregoing way from the portion or patch of the surface that falls within
the antenna's field of view. For a small aperture antenna, one of
approximately one inch (2.54 cm.) in diameter, located eight inches (20
cm.) above the ground, the field of view is an area of approximately three
square inches (7.6 square cm). Thus as the cart moves forward, the
particular patch of surface viewed or sensed by the antenna and MMW
radiometer apparatus continuously changes.
As so measured the roadway surface appears to be of a certain radiometric
temperature. As the cart positions the antenna so that the antenna views a
portion of the marker 7, the observed radiometric temperature decreases.
With further movement in which the antenna's field of view is congruent
with the marker 7, the MMW radiometric temperature observed is lower
still. As the antenna moves further to the right beyond the position of
marker 7, the temperature observed rises to the level initially observed,
representing again the roadway surface. From the foregoing observations,
thus, the downward transition in observed temperature level characterizes
the presence of marker 7, and the steady lower temperature level indicates
the presence of the marker still. The upward transition in temperature,
characterizes the right side end of the marker.
Since the position of the antenna relative to the front of the cart is
known, the antenna's height above the roadway surface is known, and the
angle at which the antenna is inclined to the roadway surface, .beta., is
known, a simple trigonometric calculation allows one to determine the
exact position in front of the cart at which the marker is located. As is
apparent to one skilled in the art, the sharpness of transition between
the roadway and the marker depends in part on the size of the field of
view of antenna 2; a smaller field of view provides a sharper transition
and essentially increases the resolution of the observed surface. For this
method, the smaller the field of view, the more accurately one can specify
the front and back edges of the marker 7 as those edges are encountered
during movement of cart 3.
The chart of FIG. 3 shows the output of a MMW radiometer that was wheeled
left to right across a parking lot roadway 5' containing stripe shaped
road markers 12a and 12b formed by painting with paint and those stripes
are overlaid upon a pictorial image of the parking lot roadway. Stripe 12a
is of the composition of the enhanced MMW radiometric paint described in
this specification and stripe 12b is formed of ordinary white roadway
marker paint and such stripes are formed atop a portion of the roadway
having a concrete surface. Similar results are obtained on an asphalt
surface.
MMW radiometric measurements were taken with the air temperature at 15
degrees Centigrade and the measurements were made by a 94 GHz radiometer
sensing the horizontally polarized radiation from the roadway at positions
12.5 inches above the roadway surface and 45 degree Nadir viewing angle,
curve 20; and 19.5 inches above the roadway surface and 22.5 degree Nadir
viewing angle, curve 22. In this figure, the ordinate is reversed in
direction and represents decreasing values; hence, a lower temperature is
represented as a higher vertical position. Considering curves 20 and 22,
it is seen that the concrete produces a certain base temperature and that
the measured temperature drops as the MMW radiometer passes over stripes
12a and 12b. As shown the decrease on stripe 12a is greater than that on
stripe 12b.
The figure also shows the effect due to raising the height of the MMW
radiometer. The temperature drops are not as pronounced as before. As
later herein described, the preferred height for the MMW radiometer
antenna input is 8 inches and the preferred viewing angle of 70 degrees,
for the particular horn 2 that is used.
As is known, reflected MMW radiometric energy is polarized. It contains a
component that is horizontally polarized and another component that is
vertically polarized. Since the MMW radiometer apparatus is capable of
selecting and measuring either polarization, one need only select one of
the two components for measuring results. It is found that the energy
received in the horizontally polarized component differs significantly
from that reflected in the vertical component, but the relationship
between measurements of like kind taken from different materials properly
correlate. Thus in making a comparison between reflections from one
material and another, one necessarily uses the same polarization in taking
measurements. In the foregoing, the horizontal (or H) polarization was
selected.
It may be seen that the sensitivity of detection is in part dependent upon
the antenna's field of view. As illustrated in FIG. 4, if the antenna's
field of view is represented by the dash line 14, the area or patch of
surface covered is significantly larger than the size of the metal marker
7' enclosed therewith. The latter marker thus has minimal influence on the
radiometric temperature detected. However where the field of view is
represented by dash line 16, a smaller patch than before, the area
occupied by the marker represents a larger percentage of that area, at
least thirty to fifty per cent of that area or more. Accordingly, the MMW
radiometric temperature detected in the latter instance is determined in
great part by the marker. Where possible, the size of the field of view
should ideally be of the same size as the smallest size road marker. Thus
the MMW radiometric temperature detected is dominated by that of the
marker. And therefore the transition or change between the temperature of
the roadway and the temperature of the marker is more pronounced as the
detector is moved from the patch of roadway to the marker.
The MMW radiometric temperature reflected from a white painted stripe on
the roadway or a more typical stripe of thermoplastic paint thereon is
different from the temperature of the adjacent roadway, whether asphalt or
concrete; and are also different from one another. Those differences are
small, but measurable. However, because the differences are small,
detection is difficult.
All electronic equipment, including MMW radiometers, receive electronic
noise or generate electronic noise internally. Implicitly, noise
interferes with the measurements. That noise may be of the same level of
the signal of interest. As a result the signal often becomes "lost" in the
noise. If possible, more sensitive and selective MMW radiometer apparatus
should be employed. That equipment however is very expensive and
impractical for use on ordinary vehicles. The better approach is to be
given stronger signals to process, thereby increasing the signal-to-noise
ratio. Thus, a marker that reflects incident MMW radiometric energy more
strongly than does the thermoplastic paint marker is of obvious benefit in
the disclosed roadway marker system. To that purpose the present invention
encompasses an enhanced MMW radiometric paint, one that produces a
stronger reflection and greater "MMW radiometric" contrast with the
adjoining roadway.
The human eye is capable of distinguishing between different graduations
between light and dark in black and white artwork found on a paper
surface. The contrast between many different shades or graduations of gray
is discernable with the naked eye. An analogous characteristic is found
with respect to different materials and the relative intensity of MMW
radiometric energy emitted and reflected by those materials, as observed
by the MMW radiometer, during exposure to MMW radiometric energy. Some
materials reflect greater intensity of incident MMW radiometric energy
than other materials. This graduation or difference in reflectivity of one
material compared to another material is referred to herein as "MMW
radiometric contrast".
Paint is often defined as a mixture of a pigment and a suitable liquid to
form an adherent coating when spread on a surface in a thin coat. The
liquid may be viscous and serves as a binder or matrix which holds the
pigment and through which the pigment is dispersed. Although the liquid
itself may reflect some color, the color reflected by the pigment
dominates. In this same sense, although the paint by itself reflects MMW
radiometric energy, an enhanced MMW radiometric paint contains particulate
matter of a material whose MMW radiometric reflecting characteristics are
significantly better than those of the carrier liquid alone. An enhanced
MMW radiometric paint improves the MMW radiometric contrast between the
marker and the adjoining roadway surface, whether the roadway is concrete
or asphalt or the like.
A first example of an enhanced MMW radiometric paint according to the
invention is as follows: A mix is prepared of the pellets or beads of
thermoplastic material, such as a vinyl, glass beads, and iron shot in the
volume ratio of 50%, 25% and 25%, respectively. The ingredients are
thoroughly mixed together to provide a homogenous mix. The glass beads are
hollow ten mil diameter spheres. The iron shot is size number 20 to 30.
The mixture is then placed in the mixing pot of a conventional road
striping apparatus, such as the "highway striper" utilized by Sterndall
Industries, and the pot is heated and raised in temperature to the
requisite temperature normally used for liquefying thermoplastic. That
liquification temperature, it is noted, is much lower than the temperature
required to soften or liquify either the glass beads or iron shot. The
thermoplastic material liquefies, while the glass beads and iron shot are
unchanged. The MMW radiometric paint is now ready for application to the
surface of the roadway, suitably formed of asphalt or concrete.
So liquified, the affixation equipment is moved to the position along the
roadway at which the marker is to be applied. The operator then releases
the liquid while moving the equipment, and the hot liquid material is
dispensed, under control of the equipment operator, typically in a wide
strip of pre-selected length and width. In California, longitudinal lines
are typically 80 mils thick and transverse lines are 125 mils thick.
Suitably, the dispensing and movement of the application equipment is such
as to deposit a one-eighth inch thick layer of the MMW radiometric paint.
Preferably, a seven mil layer of minute 4 to 20 mil diameter glass beads
are dusted on the still soft top surface of the marker to enhance the
light reflecting properties of the marker, which is the conventional
practice. As so painted on the roadway, the thermoplastic material is
allowed to cure and forms a permanent wear resistant marker with the glass
beads and iron shot encased in a thin thermoplastic binder.
In the foregoing application procedure, the striping machine operator
performs the same procedures that are used with ordinary road markers. No
special changes in application procedure are required due to the inclusion
of the iron shot.
As applied to the roadway, the MMW radiometric paint according to the
invention is illustrated in partial section view in FIG. 5. The paint 13
is bonded to the upper surface of the asphalt or concrete roadway 5 and is
between 80 mils and 1/8th inch in thickness. The glass spheres 15 and the
iron shot particles 17 are dispersed throughout the thermoplastic matrix
19. The upper surface of the paint contains a thin layer, about 7 mils
thick, of minute glass beads, 21, as is the conventional practice in
thermoplastic road markers. That forms marker 7' in place on the roadway.
FIG. 6 provides a bar chart of the radiometric temperature obtained on a
cloudy day, from a viewing angle from Nadir of 33 degrees with the air
temperature 17 degrees C. using the 94 GHz MMW radiometer. As shown, the
change in the radiometer temperature observed from the enhanced paint,
relative to the surrounding concrete roadway, is substantially greater
than from the marker formed principally of thermoplastic material; and
that of the latter is significantly greater than that of the underlying
concrete. The figure also shows what occurs when the roadway surface is
wet. The temperature measured is signficantly lower than before. However,
the incremental difference between the uncoated concrete and the enhanced
marker, is still significant.
In an alternative embodiment, an alternative to the metal shot in the
embodiment previously described, substitutes Titanium Oxide, a material
having a high dielectric constant, at least 10, in comparison to the
binder, which is about 2 to 3 in dielectric constant. This material, like
the metal, may be formed into spheroidal shapes, pellets, cylinders and
the like, and substituted for the metal. The higher dielectric material
produces a higher MMW radiometric reflectivity.
To broadly characterize the enhanced MMW radiometric paint according to the
invention, its MMW radiometric reflective characteristic should be given
in terms of a fixed viewing angle and polarization and time of day. The
MMW radiometric paint is one which, as applied to a dry flat surface as a
coating or layer exhibits a radiometric temperature that is at least 24
degrees Centigrade below the uncoated concrete roadway, when the paint is
viewed by a MMW radiometer tuned to 94 GHz and sensing only the
horizontally polarized energy and the MMW radiometer's input antenna is
oriented at twenty degrees from the normal, a twenty degree viewing angle,
with such measurement taken at mid-afternoon on a clear day.
Painted-on roadway markers, enhanced with internal particles that reflect
microwave/millimeter wave energy in the 30 to 300 GHz range, exposed to
the sky, when observed by a MMW radiometric detector, appear colder in
temperature than the adjacent asphalt or pavement forming the roadway,
particularly when viewed by the MMW radiometric apparatus at steep angles,
about 70 degrees. This contrast in temperature serves as indicium of the
presence of the marker.
The paint appears colder as a result of the balance between what is emitted
by the various materials and what they reflect. At steep observation
angles, near vertical, the enhanced paint reflects more than it emits in
comparison to the asphalt and/or concrete forming the roadway.
To minimize the possibility of adversely affecting the reliability of the
marker, essentially the physical characteristics of the thermoplastic
material, the amount of MMW radiometric particulate added to the
thermoplastic material ideally should be held to a minimum necessary to
achieve the desired result. So doing also maintains the cost of the
mixture at a minimum, enhancing cost efficiency.
Based on experimentation, it may be shown that optimum "back-scattering"
cross section achieves a maximum plateau of detectability at about the
volume fraction of 0.1. That is, when the MMW radiometric particulate is
ten percent of the mixture by volume. This optimum applies for any angle
of incidence of the MMW radiometric detector of between ten degrees and
eighty degrees from NADIR. In other words, if the percentage of MMW
radiometric particulate is increased above ten per cent, say to twenty per
cent, as example, the intensity of reflected MMW radiometric energy
detected by the MMW radiometer is no better than before. As a result of
the increased density of particles, the energy reflected by one particle
may strike an overlying particle in the solid matrix, instead of radiating
from the matrix to the detector.
Our investigation has determined that a layer thickness of one-eighth of an
inch (0.125 inch) provides near optimum back-scattering with minimal layer
thickness.
The foregoing optimum volume fraction is for a marker of 0.125 inches (0.32
cm) in thickness. For markers that are thinner, the optimum is achieved
with a higher relative volume of MMW radiometric particulate. It is
expected that the optimal volume percentages should be determined in
further investigation of the parameters for application of the invention.
The marker forms a thin film or layer atop the road surface. Although
raised slightly above the road surface, the layer's height is not
significant in comparison to automobile and vehicle tire sizes. It bears a
ratio on the order of 1 to 200 relative to a typical tire diameter. By
that comparison the layer's thickness is minuscule. That is, the layer
would not cause a thump or a perceptible bump for an automobile tire
riding over the marker. Thus, as a practical matter the marker is regarded
as being flush with the roadway surface, which is the meaning given herein
to the term "flush".
The particulate material added to the mix is not intended to and does not
significantly chemically react in the short term with the thermoplastic
materials. They are relatively chemically inert relative to those
substances. The particles are suspended in the hardened plastic, held
captive in the solid matrix.
With the enhanced MMW radiometric paint, improved roadway marker systems
using the novel method earlier described in this specification are made
more practical. Thus as pictorially illustrated in FIG. 7, a set of MMW
radiometer sensors 31 and 33 are mounted to the right and left sides of a
freight truck 30. Each of the MMW radiometer sensors contains a set of
four individual MMW radiometers, whose fields of view are individually
illustrated as four elongate ellipses. Those elliptical fields of view are
arranged essentially along side one another in a line perpendicular to the
side of the vehicle. The MMW radiometer sensor 31 on the truck's right
side as viewed by the driver monitors the relative position between the
truck and the single roadway marker 35 on one side of a roadway lane. MMW
Radiometer sensor 33 on the truck's left side monitors a set of two road
markers 37 on the truck's left side.
As represented in the block diagram of FIG. 8 the four radiometers forming
sensor 31 and those forming sensor 33 are oriented toward the ground
through a respective common focusing element, such as the respective one
of the lenses 38 and 39. Each of the MMW radiometer systems detects MMW
radiometric energy emitted and reflected from a marker encountered on the
roadway. The output signals of each of the radiometers is received and
processed by conventional electronic apparatus. The output signal from
each MMW radiometer is sent via an eight to one multiplexer 34 and from
that multiplexer to a signal digitizer 35. The digitized signal is stored
sequentially in a programmed processor 36. The processor is programmed to
monitor the position of the markers as detected by the radiometers, and to
determine if the truck is centered in the traffic lane, or has drifted to
the right or left. Should the truck have drifted to one side of the lane,
the processor initiates an appropriate warning that is sent to the driver
via a display 37.
Alternatively, in those systems that contain additional apparatus for
automatic control of vehicle steering, an output signal from the processor
can be fed to that apparatus to correct the vehicle steering. The
foregoing electronic systems are of the type earlier suggested in prior
radar type and photoelectric type control systems and need not be
described in detail. Only the "front end" MMW radiometer apparatus as the
sensor and the method for using that MMW radiometer is novel.
As pictorially illustrated in FIG. 9, where like elements to those which
appeared in FIG. 7 are denominated by the same number, the roadway marker
system may also incorporate sets of MMW radiometric markers, such as 41
and 43, that extend across the driving lane oriented perpendicular to the
truck. The spacing and widths of the markers vary in prescribed ways and
in that way carry information. The markers may be concealed, since they
are not intended to provide any visible commands or suggest any boundary,
such as would a white line across the roadway in front of a stop sign or a
lane dividing line. Each set of lateral MMW radiometric markers together
present a bar code, much like the UPC code found on boxes in the grocery
store and the Postal bar code used on mailing envelopes. As those skilled
in the bar code art are aware, the lines may be varied in width and the
spacing between lines may be varied with the first one of the lines
providing the synchronizing signal used by the decoding equipment.
As truck 30 moves across the information marker, a string of signals is
detected nearly simultaneously by all the MMW radiometers, representing
the bar code. Electronic translation apparatus carried on the truck
connected to those MMW radiometers receives and decodes the signals and
produces the translated information on a display that is visible to the
driver.
The foregoing electronic apparatus of FIG. 9 is also represented in the
block diagram of FIG. 8 to which reference is again made. The MMW
radiometer 31 and 33 outputs are multiplexed, digitized, and processed by
the programmed processor. Processor 36 includes a bar code translator,
which translates the coded information represented by stripes 41 and 43
and generates a translated message that appears on display 37. Such bar
code coding and bar code translating apparatus is well known and found in
other systems, such as universal price code UPC bar codes and postal
codes. The translator converts the received impulses into the English
language message represented thereby through use of a stored translation
dictionary. Thus the bar code that is detected may be translated as "curve
ahead", relating cautionary information to the vehicle driver and that
translated information is presented on message display 37.
A bar code pattern may thus be painted on the roadway to provide important
information to the drivers of vehicles; as example, danger, the bridge
ahead ices up in winter; railroad crossing ahead; curve ahead, trucks slow
to 35 mph; gas and food turnoff. The possibilities are numerous.
MMW radiometers offer an advantage over radar devices. The MMW radiometer
does not require a transmitter and, thereby, contains fewer parts to
build, adjust and maintain. Unlike radar, the MMW radiometer does not
irradiate the area under observation, or any persons located in the area.
Only naturally occurring radiation is used. Thus public health issues and
uncertainties regarding radiation sources and irradiation of persons is
avoided. The MMW radiometric detection functions during the day, at night,
in cloudy weather or foggy weather, and with roadways that are wet with
rainwater.
MMW radiometric enhancement is inexpensive. Existing roadway marking
affixation equipment can be used to apply the enhanced paint. No
modifications are required for the equipment. The added ingredients, such
as metal shot, are readily available and are inexpensive. Although the new
paint is of particular benefit in the novel road marker detection system
herein presented, as those skilled in the art appreciate, due to its
enhanced "visibility" at MMW frequencies, the new paint would also be of
likely benefit to the scene scanning radiometric systems, such as the
picture taking system for providing a view of an airport runway, which is
described in the Quest publication referred to in the background to this
specification, and that described in the cited patent to Caruso.
It is believed that the foregoing description of the preferred embodiments
of the invention is sufficient in detail to enable one skilled in the art
to make and use the invention. However, it is expressly understood that
the detail of the elements presented for the foregoing purpose is not
intended to limit the scope of the invention, in as much as equivalents to
those elements and other modifications thereof, all of which come within
the scope of the invention, will become apparent to those skilled in the
art upon reading this specification. Thus the invention is to be broadly
construed within the full scope of the appended claims.
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